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Top End Notes Part 2 - Piston

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Seems that the stock piston is pretty durable; at least the way we use it. The new piston spec is 77.97 mm - 77.98 mm with a service limit of 77.89 mm. Our piston after 99.5 hours measured out at 77.95 mm. And 80+ of those hours were with the CCC mods and 13,000+ rpm rev limit. Unfortunately, I forgot to measure the ring gap of the old rings :bonk: . We replaced the old piston with a 13.5:1 JE :thumbsup: . The old piston looks pretty good, but that JE is mighty nice :thumbsup: :

Exhaust Side

Intake Side

"Left" Side

"Right" Side

Top

As background, the bike began to use oil (and put it in the catch tube) at 10 hours when I did the CCC mods and jetted way too rich (I had a 170 MJ and needed a 148). I never saw puffs of smoke from the exhaust (and I always look on startup), so the oil useage must have been slow and continual. After I rejetted properly, the oil use stopped for quite a while, then came back. At rebuild time, the engine was using around 1/8" - 1/4" on the stick every 3 - 6 hours, but it wasn't consistent. The oil doesn't seem to have been coming through the intake guides as the back side of the intake valves are clean. When I pulled the piston, the ring gaps weren't aligned. There's no evidence of blow-by between the top and oil rings, but there is a lot of crud on the top of the piston. I suspect the oil use was around the rings, but without the old ring gaps, I can't be sure. I used a lot of HP4M with this piston so I could be seeing the combustion chamber contamination and oil useage that kelstr mentioned.

Based on these observations, I'm going to keep the jetting right, and use only Rotella T for the new JE piston we put in.

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Here is mine at 70 hours

Intake side of piston

valve

Mine would blow the blue smoke at start up every once in a while. I am guessing the valve guides were going and the rings were getting there by the scuffing & blow by on the side of the piston.

I rode for about an hour yesterday with the new JE Piston, Hot Cam, R head :thumbsup: . Its making some awesome power. I need to fatten up the jetting as its leaning out at 3/4 throttle. I may wait till it warms up a bit as it was 24 degrees out riding yesterday.

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Do you have to run octane booster or race gas with the 13:5:1 skipn8er, or will it run on straight pump gas?

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Do you have to run octane booster or race gas with the 13:5:1 skipn8er, or will it run on straight pump gas?

I live at 5,300 ft and we have lower octane requirements than sea level. Like Dennis, I've read that the 13.5:1 will run fine at sea level with good pump gas (91+ octane). I've only run 100+ octane so far with no problems; not for the octane, but for the cleanliness.

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Seems that the stock piston is pretty durable; at least the way we use it. The new piston spec is 77.97 mm - 77.98 mm with a service limit of 77.89 mm. Our piston after 99.5 hours measured out at 77.95 mm. And 80+ of those hours were with the CCC mods and 13,000+ rpm rev limit. Unfortunately, I forgot to measure the ring gap of the old rings :bonk: . We replaced the old piston with a 13.5:1 JE :thumbsup: . The old piston looks pretty good:

Exhaust Side

Intake Side

"Left" Side

"Right" Side

Top

As background, the bike began to use oil (and put it in the catch tube) at 10 hours when I did the CCC mods and jetted way too rich (I had a 170 MJ and needed a 148). I never saw puffs of smoke from the exhaust (and I always look on startup), so the oil useage must have been slow and continual. After I rejetted properly, the oil use stopped for quite a while, then came back. At rebuild time, the engine was using around 1/8" - 1/4" on the stick every 3 - 6 hours, but it wasn't consistent. The oil doesn't seem to have been coming through the intake guides as the back side of the intake valves are clean. When I pulled the piston, the ring gaps weren't aligned. There's no evidence of blow-by between the top and oil rings, but there is a lot of crud on the top of the piston. I suspect the oil use was around the rings, but without the old ring gaps, I can't be sure. I used a lot of HP4M with this piston so I could be seeing the combustion chamber contamination and oil useage that kelstr mentioned.

Based on these observations, I'm going to keep the jetting right, and use Rotella T for the new JE piston we put in.

yes that has the look of some Molly burnt on it ( was there alot in the exhaust side of the head and on the head also? ) but it really is not as bad compared to most i get through the shop,

dennit1's piston is what i usually see coming through the shop where it has not ever had a good ring seal,

and was running Molly or like an amsoil man made syn in it.

when you get your je in like dennit1 you will love the thing like he does, the je just stays supported better with the better skirt and will live even better, i have just put rings on one je that had over 100 hrs on the poor thing to just see how long one will go,--it is still ripping ! :thumbsup:

it is amazing how well the pistons live in these little things at 13,000,

i really thought these would never live as long as they do, but they go like hell :bonk:

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Ron Hamp said pump gas is ok.

yes they work fine on pump,

we have some of the worst pump in any state in the union here in az,

and the little honda works fine with our 91 in it ( which is really at 89 :bonk: )

and at 1200 feet they don't detonate in 110 degree weather,

but when you run our 87 ( which is 84 :thumbsup::thumbsup::bonk: )

they will hammer the lower rod bearing out in short order with the 13.5 or even stock piston in them :bonk:

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